Philadelphia-area residents are likely to wake up to a frosty morning Thursday, forecasters say.

The National Weather Service has issued a frost advisory for western Chester County, western Montgomery County and upper Bucks County, as well as some places north and parts of northwest New Jersey, for early Thursday morning.

"Several nights of potential frost or freezing temperatures are on the horizon for portions of eastern Pennsylvania and New Jersey," the advisory says.

The weather service says temperatures are expected to drop into the mid-30s by Thursday morning, and parts of the Poconos could see below-freezing temperatures.

The frost advisory is in effect from 2 a.m. to 9 a.m. Thursday.

The cool temperatures are expected to continue for the next several days, and forecasters say a "more widespread frost or freeze is possible early Friday and again early Saturday morning" throughout eastern Pennsylvania, Delaware and New Jersey.

Even lower temperatures are forecasted for much of central and northeast Pennsylvania, which are under freeze watches or warnings.

In Philadelphia, forecasters say to expect cloudy skies today with a chance of rain, particularly before 3 p.m. The high is expected to be 55 degrees, with an overnight low of 38 expected.

The last time the temperature dipped that low in Philadelphia was April 22.

The weather service is calling for a high of 54 degrees on both Thursday and Friday, with overnight lows of 37 and 36 degrees expected.

Those temperatures are significantly below normal lows for the week, which are between 45 and 47 degrees.

Still, it's not entirely unusual for temperatures to reach that level this early: The mercury drops to 36 degrees or below in Philadelphia by Oct. 26 -- Saturday -- 50 percent of the time, according to weather service data.